If you are a loyal blackra1n user who kept the blackra1n.app on your iPhone, run it. You will see Icy replaced by an option "ra1n". Install this to upgrade your app. After upgrading, run blackra1n.app again. You will see "sn0w". Install this, and enjoy your unlocked iPhone.
If you are new to the scene, just looking for an unlock, finally ready to upgrade to 3.1.2 and the accompanying baseband, willing to restore for the latest and greatest, or stuck on the "Connect to iTunes" screen, you are in luck. Jailbreaking and unlocking have never been easier. Go to blackra1n.com, click on the logo corresponding to your operating system, run the app, and click "make it ra1n". When your phone reboots, you'll see blackra1n.app. Run this, install blacksn0w, and enjoy your unlocked iPhone
Trích từ
http://iphonejtag.blogspot.com/2009/11/sn0wday.html